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Bressay Field Viscosity

In late 2018 a thirty-year adventure will begin 250 kilometres off Scotland’s north-east coast. That’s when the first oil tanker will leave the Mariner field, bound for the world’s energy markets. It’s been a long journey. Mariner is a sleeping giant, discovered more than thirty years ago. 

But because of the oil’s extremely high viscosity, previous operators were not able to extract it. In 2007, we acquired the operatorship, and with the experience gained from working with other heavy oil fields, we managed to solve the challenges. The Mariner project will be one of Statoil’s most innovative developments ever.

Discovered in 1981 on the East Shetland Platform, approximately 150 kilometres east of the Shetland Islands, the Mariner field is a daunting prospect for oil and gas producers. Mariner is a heavy oil field characterised by dense, viscous oil.

In December 2012, Statoil and its partners decided to take on the challenge and made the investment decision for the Mariner project, which entails a gross investment of more than GBP 4.5 billion. This was the largest capital commitment to the UK Continental Shelf (UKCS) in more than a decade.

The concept chosen includes a production, drilling and quarters (PDQ) platform based on a steel jacket, Mariner A, with a floating storage unit (FSU), Mariner B. Drilling will be carried out from the Mariner A drilling rig, with a jack-up rig assisting for the first 4 years.

The Mariner oil field consists of two shallow reservoir sections: the deeper, Maureen formation at 1492 meters and the shallower Heimdal reservoir at 1227 meters. The oil is heavy with API gravities of 14.2 and 12.1 and viscosities at reservoir conditions of 67 cP and 508 cP, respectively for Maureen and Heimdal.  

The development of the Mariner field will contribute more than 250 mmbbls reserves with average plateau production of around 55,000 barrels per day. The field will provide a long term cash-flow over 30 years.  Production is expected to commence in 2018.

The Bentley Oil Field is a heavy oil field located on the East Shetland Platform in the UK Northern North Sea, 8 kilometres (5.0 mi) southeast of the Bressay Field (operator: Statoil), 15 kilometres (9.3 mi) east of the Kraken Field (operator: EnQuest) and 20 kilometres (12 mi) north-northeast of the Bruce Field (operator: BP).


The Bentley Field, located on the UK continental shelf in block 9/3b in 110 m of water, contains approximately 900 MMstb in-place of heavy (10 to 12 oAPI) viscous (1500 cP) crude. The field is four-way dip closed at uppermost Palaeocene, lowermost Eocene, Dornoch sandstone level, and covers an area of about 16 km by 5 km at a depth of around 1.1 km TVDss. The reservoir is high porosity (33%), net to gross pay (90%) and with ultra-high apparent horizontal permeabilities approaching 50 Darcies based on flow-test measurements, but consistent with unconsolidated sand. [1]

Appraisal History[edit]

The field was discovered in 1977 with the Amoco 9/3-1 vertical exploration well, which discovered an 81 ft oil column in high quality Dornoch sandstone. The field was subsequently licensed to Conoco who appraised it with two further vertical wells (9/3-2A and 9/3-4) in the 1980s. These confirmed the presence of a large accumulation, estimated at that time to be similar to today’s figure at around 900 MMstb in-place. Attempts to gas-lift the 9/3-1 well failed due to the viscous nature of the Bentley crude, whilst an attempt to flow 9/3-2A using a downhole pump failed due to mechanical reasons.

With two failed tests and an oil price below $20/bbl Conoco relinquished the license in the mid 1990s.

There was no further activity on the block until 2003 when Xcite applied for, and were awarded, a Promote License on the block during the UK 21st Licensing Round. This was the first licensing round in which Promote Licences had been awarded and represented an important initiative from the UK licensing authorities to encourage small and new-start companies to acquire and promote acreage. The license was converted to a Traditional License in 2005 prior to Xcite’s first appraisal well (9/03b-5) in 2008.[2]

This well was a vertical appraisal well, drilled at the end of 2007 and successfully flow-tested in January 2008. This was followed two more wells drilled November 2010 (9/03b-6 and 9/03b-6Z) to identify reservoir structure and characterise reservoir properties. The resultant flow-test delivered a surface constrained, final stabilised rate of 2,900 stb/day.

In August 2012 a successful extended well test was performed to gather more data on the reservoir properties and water cut by using the jack-upRowan Norway. In October 2012 after 60 days, Xcite Energy announced the successful conclusion of the extended well test, with the 9/3b-7 and 7Z wells successfully suspended for future use as production wells. [3]

The Bentley crude oil produced during the extended well test was stored on a floating storage unitScott Spirit, and was sold to BP as per the off take agreement. [4]


The recoverable reserves are estimated at 267 million barrels (42.4×106 m3) of heavy oil (API 10-12) and total oil in place is in excess of 880 million barrels (140×106 m3).[5]


Since 2013 Xcite Energy Resources has been working with and signed memorandums of understanding with a number of industry partners to do pre-FEED/assurance engineering prior to arranging financing. The industry partners include AMEC, ARUP,[6] Teekay Shipping,[7] AIBEL AS,[8] Baker Hughes[9] and China Oilfield Services Limited.[10] The company has also signed a collaboration agreement with Statoil and Shell in May 2014[11] to make available and share field-specific technical and operational information for the evaluation of potential synergies and collaboration between the Bentley and Bressay Fields, and another collaboration agreement in October 2014 with EnQuest and Statoil[12] in order to evaluate the potential utilisation of common gas import infrastructure between the Kraken, Bentley and Bressay fields.

In October 2015 the Bentley license was reviewed in order to ascertain the appropriate field determination boundary for agreement with the OGA and the boundary of the Bentley oil field has been accepted subject to formal FDP approval.

Xcite announced in February 2016 that they had successfully completed a technical review of the first phase of the Bentley field development with the Oil and Gas Authority to ensure that the plan meets the OGA's policy objectives of maximising the economic benefit to the UK of its oil and gas resources. At the same time the company announced that they anticipate submitting a field development plan to the OGA in 2016.[13]

The Bentley field is planned with a phased development. The first phase development, with a 5-year drilling programme, and focused on the northern area of the field will be followed by a second phase, which will focus on the western and south areas of the Bentley field. As the Bentley development will be short of fuel gas for meeting its power generation and process heat requirements, the first phase development plans is to include a 10 km 6" pipeline from a tie-in to the Kraken field for fuel gas import.[14]

Technical and engineering work streams are largely complete and it is expected that the field will commence operation approximately three years after FDP approval from the UK Government. FDP submission is currently pending commercial and funding discussions which are ongoing as of May 2016. The company announced in their 2015 third quarter results that technical and commercial due diligence on the Bentley field had been completed by a potential field development partner, but that they remained very actively engaged with a wide range of parties in order to maximise the opportunity to secure the required funding. Separately, the that the company has committed a significant amount of time to a technical review of the Bentley field development concept with the United Kingdom Oil and Gas Authority.[15]

In late May 2016 Xcite Energy announced that they had reached agreement on the principal commercial terms for the development funding of the first phase of the Bentley project, but that they require a partner to join the development group. Separately, the company is running a tender process to select an EPCIC contractor for the MOPU and FSO and to finalise a drilling rig contract.[16]


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